1. Technical Field
Embodiments of the present invention relate to an optical network unit that is capable of reducing OBI (optical beat interference), and to a method of controlling the optical network unit.
2. Description of the Related Art
An OFDMA-PON (orthogonal frequency division multiplexing access-passive optical network) system is a system in which a multiple number of optical network units (ONU) have a main carrier (optical carrier) of the same wavelength, with each of the optical network units allotted with subcarriers of different orthogonal relationships. Thus, each optical network unit may have to use a photoelectric converter part, such as a laser diode (LD) for instance, of the same wavelength.
However, since the resonator length of a laser diode has to be adjusted with high precision at the level of the wavelengths of light, it is extremely difficult to produce several laser diodes that emit wavelengths that are physically completely identical. What is more, the refractive index of the gain medium may be changed according to the magnitude of the bias current and according to temperature, resulting in slight changes in the center wavelength of the laser diode as well.
FIG. 1 schematically illustrates a problem that may occur in a conventional OFDMA-PON system. Referring to FIG. 1, a difference in the wavelengths of the main carriers between the optical network units can generate optical interference noise if the central office (CO) or the optical line termination (OLT) installed therein uses a direct detection system. If optical interference noise is present in a subcarrier signal band carrying data, the signal-to-noise ratio (SNR) may be adversely lowered, resulting in degraded performance of the system.